The present invention relates to a pneumatic tire with a designated fitting direction relative to a vehicle, or more specifically to a pneumatic tire capable of improving a wet performance and reducing vehicle exterior noise while ensuring a dry performance.
A dry performance of a pneumatic tire is degraded when raising a groove area ratio on a tread portion in order to improve a wet performance of the tire. On the other, vehicle exterior noise tends to be increased when a lug groove component on the tread portion is increased in order to improve the wet performance. Accordingly, it is difficult to satisfy all demands for improvements in the dry performance, the wet performance, and the reduction in vehicle exterior noise at the same time.
Conventionally, in order to achieve a good balance among the dry performance, the wet performance, and the reduction in vehicle exterior noise, there has been proposed a pneumatic tire having a designated rotational direction when being mounted on a vehicle, the pneumatic tire including multiple main grooves formed on a tread portion so as to extend in a circumferential direction of the tire, and multiple sub-grooves inclined from a tread center region toward corresponding shoulder regions mutually in opposite directions relative to the circumferential direction of the tire. Here, a center rib is disposed in the tread center region while shoulder block rows are disposed in the shoulder regions. Moreover, other block rows are disposed inward of the shoulder block regions and shapes and layouts of the sub-grooves are thus defined (see, for example, Japanese patent application Kokai publication No. 7-164829).
Nevertheless, in the reality, the above-described pneumatic tire is not able to sufficiently respond to demands for improvements today. Meanwhile, there have been disclosed various pneumatic tires with a designated fitting direction relative to a vehicle, which are designed to achieve improvements in tire performances based on the designated fitting direction (see, for example, Japanese patent application Kokai publication No. 2007-15655). However, such pneumatic tires also face difficulties to satisfy the demands for improvements in the dry performance, the wet performance, and the reduction in vehicle exterior noise at the same time.